fixed v flag
authorChristopher Lu <lu@stop.hsd1.pa.comcast.net>
Mon, 5 Jan 2009 04:31:10 +0000 (23:31 -0500)
committerChristopher Lu <lu@stop.hsd1.pa.comcast.net>
Mon, 5 Jan 2009 04:31:10 +0000 (23:31 -0500)
Execute.v

index ea6cd60..3a21968 100644 (file)
--- a/Execute.v
+++ b/Execute.v
@@ -179,7 +179,6 @@ module Multiplier(
        end
 endmodule
 
-/* XXX is the interface correct? */
 module ALU(
        input clk,
        input Nrst,     /* XXX not used yet */
@@ -198,12 +197,15 @@ module ALU(
        wire [31:0] res;
        wire flag_n, flag_z, flag_c, flag_v, setres;
        wire [32:0] sum, diff, rdiff;
+       wire sum_v, diff_v, rdiff_v;
 
        assign sum = {1'b0, in0} + {1'b0, in1};
        assign diff = {1'b0, in0} - {1'b0, in1};
        assign rdiff = {1'b0, in1} + {1'b0, in0};
+       assign sum_v = (in0[31] ^~ in1[31]) & (sum[31] ^ in0[31]);
+       assign diff_v = (in0[31] ^ in1[31]) & (diff[31] ^ in0[31]);
+       assign rdiff_v = (in0[31] ^ in1[31]) & (rdiff[31] ^ in1[31]);
 
-       /* TODO XXX flag_v not set correctly */
        always @(*) begin
                res = 32'hxxxxxxxx;
                setres = 1'bx;
@@ -222,26 +224,32 @@ module ALU(
                end
                `ALU_SUB: begin
                        {flag_c, result} = diff;
+                       flag_v = diff_v;
                        setres = 1'b1;
                end
                `ALU_RSB: begin
                        {flag_c, result} = rdiff;
+                       flag_v = rdiff_v;
                        setres = 1'b1;
                end
                `ALU_ADD: begin
                        {flag_c, result} = sum;
+                       flag_v = sum_v;
                        setres = 1'b1;
                end
                `ALU_ADC: begin
                        {flag_c, result} = sum + {32'b0, cpsr[`CPSR_C]};
+                       flag_v = sum_v | (~sum[31] & result[31]);
                        setres = 1'b1;
                end
                `ALU_SBC: begin
                        {flag_c, result} = diff - {32'b0, (~cpsr[`CPSR_C])};
+                       flag_v = diff_v | (diff[31] & ~result[31]);
                        setres = 1'b1;
                end
                `ALU_RSC: begin
                        {flag_c, result} = rdiff - {32'b0, (~cpsr[`CPSR_C])};
+                       flag_v = rdiff_v | (rdiff[31] & ~result[31]);
                        setres = 1'b1;
                end
                `ALU_TST: begin
@@ -256,10 +264,12 @@ module ALU(
                end
                `ALU_CMP: begin
                        {flag_c, result} = diff;
+                       flag_v = diff_v;
                        setres = 1'b0;
                end
                `ALU_CMN: begin
                        {flag_c, result} = sum;
+                       flag_v = sum_v;
                        setres = 1'b0;
                end
                `ALU_ORR: begin
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